Chapter 9 - Depth of Understanding

Discuss the clinical relevance of the flagella and the glycocalyx.

The five requirements for infection are getting in, staying in, defeating the host defence, damaging the host and being transmissible. The clinical significance of the glycocalyx results from its adherence properties and inhibition of phagocytosis. Both the slime layer and capsule forms of the glycocalyx are important in the adherence of pathogens to surfaces such as the respiratory and urinary tract. The capsule form of the glycocalyx is required for infection in some bacteria, such as Streptococcus pneumoniae which is not infectious unless encapsulated, and enables defeat of the host defences by inhibiting phagocytosis. Flagella have clinical significance through attachment properties and pathogen motility. Flagella can enable pathogens to move from the initial portal of entry, to avoid host defences such as phagocytic cells by moving away from them, and allow movement from tissues into the blood and lymph where the pathogen can travel around the body and generate a systemic infection. An example is Helicobacter pylori, its powerful flagellar movements allow it to bury itself in the mucosa of the stomach, where it is protected from the acidic stomach environment.

Compare and contrast the Gram-positive and Gram-negative cell wall.

The major differences in the cell wall of Gram-positive and Gram-negative bacteria are the amounts of peptidoglycan (a much thicker layer occurs in Gram-positive bacteria), the presence of teichoic acid in Gram-positive bacteria, and the presence of an outer membrane including a lipopolysaccharide layer which occurs in Gram-negative bacteria.

Describe the problems associated with endospore formation.

Any pathogen that can form an endospore is problematic. The only way to destroy endospores is by the combination of high heat and high pressure. The endospore is resistant to almost all forms of antisepsis and disinfection and therefore can remain in areas of the clinic and continue to pose a threat of infection. There are no clinical disadvantages to being able to form an endospore.